This proposal seeks to continue the development of a reliable implantable sensor for glucose. Such a device will be used in conjunction with an artificial pancreas consisting of the sensor, a microprocessor driven data acquisition and control system and a pump which will infuse insulin as needed. Such a device is intended to provide good glycemic control thereby avoiding the complications associated with insulin-dependent diabetes. A major missing link is a reliable sensor for blood glucose. To improve reliability it is first proposed to further explore the possibility of subcutaneous (Sub-Q) measurements. By in-vivo measurements it will be established in conscious dogs that the measured Sub-Q levels can be made a reliable indicator for glycemic control. A miniature needle-type enzyme electrode (less than lmm O.D.) sensor will be prepared with a geometry which permits easy and reproducible fabrication of the reactive (selective) and protective layers and which can be readily inserted under the skin. New methods are proposed for immobilization of the enzyme in highly active and stable form. Enzyme response will be coupled efficiently to the electrode so as to avoid interferences from the biological medium. Finally, a portable microprocessor-based data acquisition and control system (500g) will be developed for use with dogs. Its primary purpose is to permit in-vivo evaluation of sensors, but it will be readily adapted to the artificial pancreas.